The field of the present invention is devices for defining the timing edge on ports of two-cycle engines.
Two-cycle engines typically include one or more cylinders each having an exhaust port through the wall thereof and a piston slidably working within the cylinder so as to alternately expose and cover over the exhaust port. In such an arrangement, the opening and closing of the exhaust port by the piston is defined by the upper edge of the piston and the upper edge of the exhaust port.
Devices have been developed which include a valve mechanism defining an adjustable upper exhaust port edge. Typically the valve mechanism includes an element defining a timing edge. The element is adjustable in the axial direction of the cylinder responsive to engine speed. Two-cycle engines often have tuned exhausts such that a pressure wave generated with the opening of the exhaust port rebounds back to the port just prior to the closing of the exhaust port to compress exiting air/fuel mixture back into the combustion chamber. To utilize this phenomenon, the higher the engine speed, the sooner the exhaust valve must open and the later the exhaust valve must close. Naturally, the reverse is true for lower engine speeds.
The environment in which such exhaust timing control mechanisms operate is both demanding and adverse. Temperatures of the exhaust gases are high and the exhaust gases are dirty and tend to accumulate carbon materials in the components. The valve mechanism must also move rapidly and freely to reflect changing engine conditions and preferably provides a good seal between the timing edge and the cylinder wall above in order that effective timing control may be realized.